一种基于MMS的改进降水径流模型在中国西北地区黑河上游流域的应用

以黑河流域上游为研究对象,通过对山区自然产水区的产汇流机理的研究,基于分布式水文模型集成环境的开发思想,利用MMS(modular modeling system)模型库中与降水径流相关的模块,通过综合各种产流(包括超渗、蓄满产流)机理、并且根据寒区产汇流的特点对USGS开发的流域PRMS(precipitation-runoff models)模型进行了改进,增加了土壤水运动中降雨入渗补给的多层土壤滞后效应模块以及积雪融雪和冻土面积识别模型,建立了适合于寒区流域的分布式PRMS模型。利用该模型对黑河上游出山径流过程进行了模拟与预报,模型研究结果表明:利用MMS建立的黑河上游改进的PRMS模型不仅完全可以模拟和预测黑河上游的产汇流过程,在考虑了冻土的情况下,预测年出山径流量误差小于2.7%;而且模型可以对黑河上游径流组成成分进行分析计算,对黑河上游产汇流机理做进一步阐明。利用改进的PRMS模型,预测分析了黑河上游未来气候和土地覆盖变化情景下流域出山径流变化的趋势,为黑河流域水资源合理利用和管理提供科学依据。     

An analysis of urban development and its environmental impact on the Tampa Bay watershed

Urbanization has transformed natural landscapes into anthropogenic impervious surfaces. Urban land use has become a major driving force for land cover and land use change in the Tampa Bay watershed of west-central Florida. This study investigates urban land use change and its impact on the watershed. The spatial and temporal changes, as well as the development density of urban land use are determined by analyzing the impervious surface distribution using Landsat satellite imagery. Population distribution and density are extracted from the 2000 census data. Non-point source pollution parameters used for measuring water quality are analyzed for the sub-drainage basins of Hillsborough County. The relationships between 2002 urban land use, population distribution and their environmental influences are explored using regression analysis against various non-point source pollutant loadings in these sub-drainage basins. The results suggest that strong associations existed between most pollutant loadings and the extent of impervious surface within each sub-drainage basin in 2002. Population density also exhibits apparent correlations with loading rates of several pollutants. Spatial variations of selected non-point source pollutant loadings are also assessed.     

Community analysis of ammonia-oxidizing bacteria in activated sludge of eight wastewater treatment systems

We investigated the communities of ammonia-oxidizing bacteria(AOB) in activated sludge collected from eight wastewater treatment systems using polymerase chain reaction(PCR) followed by terminal restriction fragment length polymorphism(T-RFLP),cloning,and sequencing of the α-subunit of the ammonia monooxygenase gene(amoA).The T-RFLP fingerprint analyses showed that different wastewater treatment systems harbored distinct AOB communities.However,there was no remarkable difference among the AOB TRFLP profiles from different parts of the same system.The T-RFLP fingerprints showed that a full-scale wastewater treatment plant(WWTP) contained a larger number of dominant AOB species than a pilot-scale reactor.The source of influent affected the AOB community,and the WWTPs treating domestic wastewater contained a higher AOB diversity than those receiving mixed domestic and industrial wastewater.However,the AOB community structure was little affected by the treatment process in this study.Phylogenetic analysis of the cloned amoA genes clearly indicated that all the dominant AOB in the systems was closely related to Nitrosomonas spp.not to Nitrosospira spp.Members of the Nitrosomonas oligotropha and Nitrosomonas communis clusters were found in all samples,while members of Nitrosomonas europaea cluster occurred in some systems.     

A comparative study in treating two VOC mixtures in trickle bed air biofilters

Two independent parallel trickling bed air biofilters (TBABs) ("A" and "B") with two different typical VOC mixtures were investigated. Toluene, styrene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) were the target VOCs in the mixtures. Biofilter "A" was fed equal molar ratio of the VOCs and biofilter "B" was fed a mixture based on EPA 2003 emission report. Backwashing and substrate starvation operation were conducted as biomass control. Biofilter "A" and "B" maintained 99% overall removal efficiency for influent concentration up to 500 and 300 ppmv under backwashing operating condition, respectively. The starvation study indicated that it can be an effective biomass control for influent concentrations up to 250 ppmv for biofilter "A" and 300 ppmv for "B". Re-acclimation of biofilter performance was delayed with increase of influent concentration for both biofilters. Starvation operation helped the biofilter to recover at low concentrations and delayed re-acclimation at high concentrations. Furthermore, re-acclamation for biofilter "B" was delayed due to its high toluene content as compared to biofilter "A". The pseudo first-order removal rate constant decreased with increase of volumetric loading rate for both biofilters. MEK and MIBK were completely removed in the upper 3/8 media depth. While biofilter depth utilization for the removal of styrene and toluene increased with increase of influent concentrations for both biofilters. However, toluene removal utilized more biofilter depth for biofilter "B" as compared to biofilter "A".     

Ecological metrics of biomass removed by three methods of purse-seine fishing for tunas in the eastern tropical Pacific Ocean

An ecosystem approach to fisheries management is a widely recognized goal, but describing and measuring the effects of a fishery on an ecosystem is difficult. Ecological information on the entire catch (all animals removed, whether retained or discarded) of both species targeted by the fishery and nontarget species (i.e., bycatch) is required. We used data from the well-documented purse-seine fishery for tunas (Thunnus albacares, T. obesus, and Katsuwonus pelamis) in the eastern tropical Pacific Ocean to examine the fishery's ecological effects. Purse-seine fishing in the eastern tropical Pacific is conducted in 3 ways that differ in the amount and composition of target species and bycatch. The choice of method depends on whether the tunas are swimming alone (unassociated sets), associated with dolphins (dolphin sets), or associated with floating objects (floating-object sets). Among the fishing methods, we compared catch on the basis of weight, number of individuals, trophic level, replacement time, and diversity. Floating-object sets removed 2-3 times as much biomass as the other 2 methods, depending on how removal was measured. Results of previous studies suggest the ecological effects of floating-object sets are thousands of times greater than the effects of other methods, but these results were derived from only numbers of discarded animals. Management of the fishery has been driven to a substantial extent by a focus on reducing bycatch, although discards are currently 4.8% of total catch by weight, compared with global averages of 7.5% for tuna longline fishing and 30.0% for midwater trawling. An ecosystem approach to fisheries management requires that ecological effects of fishing on all animals removed by a fishery, not just bycatch or discarded catch, be measured with a variety of metrics.     

Long term performance of MBR for biological nitrogen removal from synthetic municipal wastewater

This study monitors the long term performance of membrane bioreactor (MBR) for the treatment of synthetic municipal wastewater at solid retention time (SRT) of 40 and 20d with particular emphasis on simultaneous nitrification-denitrification (SND). SND was greatly influenced by the operating dissolved oxygen (DO). It was found that at an SRT of 20d, nitrogen removal through assimilation into biomass increases as a result of higher biomass yield. The profile of soluble microbial products (SMP) conformed to a cyclical pattern in the MBR with respect to SRT. Decrease in SRT from 40 to 20d resulted in doubling of accumulated SMP concentration (to 56mgl(-1)) in the MBR. This however, was accompanied by a simultaneous drop in percentage of SMP with MW>100kD, from 42.4% to 33%. Also, the sludge filterability decreased by 24-folds despite a decrease in the biomass concentration, following the above reduction in SRT. It was found that the volumetric oxygen transfer coefficient (K(l)a) was a function of biomass concentration in MBR with the ratio of the oxygen transfer coefficient in mixed liquor to that of clean water (alpha) to be 0.2-0.5.     

Atmospheric mercury monitoring survey in Beijing,China

With the aid of one industrial, two urban, two suburban, and two rural sampling locations, diurnal patterns of total gaseous mercury (TGM) were monitored in January, February and September of 1998 in Beijing, China. Monitoring was conducted in six (two urban, two suburban, one rural and the industrial sites) of the seven sampling sites during January and February (winter) and in four (two urban, one rural, and the industrial sites) of the sampling locations during September (summer) of 1998. In the three suburban sampling stations, mean TGM concentrations during the winter sampling period were 8.6, 10.7, and 6.2 ng/m3, respectively. In the two urban sampling locations mean TGM concentrations during winter and summer sampling periods were 24.7, 8.3, 10, and 12.7 ng/m3, respectively. In the suburban-industrial and the two rural sampling locations, mean mercury concentrations ranged from 3.1-5.3 ng/m3 in winter to 4.1-7.7 ng/m3 in summer sampling periods. In the Tiananmen Square (urban), and Shijingshan (suburban) sampling locations the mean TGM concentrations during the summer sampling period were higher than winter concentrations, which may have been caused by evaporation of soil-bound mercury in warm periods. Continuous meteorological data were available at one of the suburban sites, which allowed the observation of mercury concentration variations associated with some weather parameters. It was found that there was a moderate negative correlation between the wind speed and the TGM concentration at this suburban sampling location. It was also found that during the sampling period at the same site, the quantity of TGM transported to or from the sampling site was mainly influenced by the duration and frequency of wind occurrence from certain directions.     

Determination of the potential for release of mercury from combustion product amended soils: Part 1--Simulations of beneficial use

This paper describes a project that assessed the potential for mercury (Hg) release to air and water from soil amended with combustion products to simulate beneficial use. Combustion products (ash) derived from wood, sewage sludge, subbituminous coal, and a subbituminous coal-petroleum coke mixture were added to soil as agricultural supplements, soil stabilizers, and to develop low-permeability surfaces. Hg release was measured from the latter when intact and after it was broken up and mixed into the soil. Air-substrate Hg exchange was measured for all materials six times over 24 hr, providing data that reflected winter, spring, summer, and fall meteorological conditions. Dry deposition of atmospheric Hg and emission of Hg to the atmosphere were both found to be important fluxes. Measured differences in seasonal and diel (24 hr) fluxes demonstrated that to establish an annual estimate of air-substrate flux from these materials data on both of these time steps should be collected. Air-substrate exchange was highly correlated with soil and air temperature, as well as incident light. Hg releases to the atmosphere from coal and wood combustion product-amended soils to simulate an agricultural application were similar to that measured for the unamended soil, whereas releases to the air for the sludge-amended materials were higher. Hg released to soil solutions during the Synthetic Precipitation Leaching Procedure for ash-amended materials was higher than that released from soil alone. On the basis of estimates of annual releases of Hg to the air from the materials used, emissions from coal and wood ash-amended soil to simulate an agricultural application could simply be re-emission of Hg deposited by wet processes from the atmosphere; however, releases from sludge-amended materials and those generated to simulate soil stabilization and disturbed low-permeability pads include Hg indigenous to the material.     

Role of biological activity and biomass distribution in air biofilter performance

The effects of temporal and spatial changes in biological activity and biomass amount on biofilter performance were investigated in a lab-scale trickle-bed air biofilter at a toluene loading of 46.9gm(-3)h(-1) under two different experimental strategies, namely, periodic backwashing at a rate of 1h once a week and 2d starvation. Analysis of the overall reaction for toluene metabolism revealed that cell synthesis was relatively favored over toluene oxidation in the inlet section of the biofilter, but over time its oxidation became favored throughout the biofilter bed. Periodic in situ backwashing with media fluidization effectively made even spatial distribution of biomass along the bed media, by which consistent high removal performance in the biofilter has been attained. After 2d starvation, the ratio of the biofilm EPS to the total biomass increased along the media bed depth, while the total biomass in the media bed subsequently decreased. The presence of sufficient biomass and microbial activity favorably influenced biofilter reacclimation after restart-up following starvation.     

Marine reserves,fisheries ban,and 20 years of positive change in a coral reef ecosystem

By 2004, Belize was exhibiting classic fishing down of the food web. Groupers (Serranidae) and snappers (Lutjanidae) were scarce and fisheries turned to parrotfishes (Scarinae), leading to a 41% decline in their biomass. Several policies were enacted in 2009–2010, including a moratorium on fishing parrotfish and a new marine park with no-take areas. Using a 20-year time series on reef fish and benthos, we evaluated the impact of these policies approximately 10 years after their implementation. Establishment of the Southwater Caye Marine Reserve led to a recovery of snapper at 2 out of 3 sites, but there was no evidence of recovery outside the reserve. Snapper populations in an older reserve continued to increase, implying that at least 9 years is required for their recovery. Despite concerns over the feasibility of banning parrotfish harvest once it has become a dominant fin fishery, parrotfishes returned and exceeded biomass levels prior to the fishery. The majority of these changes involved an increase in parrotfish density; species composition and adult body size generally exhibited little change. Recovery occurred equally well in reserves and areas open to other forms of fishing, implying strong compliance. Temporal trends in parrotfish grazing intensity were strongly negatively associated with the cover of macroalgae, which by 2018 had fallen to the lowest levels observed since measurements began in 1998. Coral populations remained resilient and continued to exhibit periods of net recovery after disturbance. We found that a moratorium on parrotfish harvesting is feasible and appears to help constrain macroalgae, which can otherwise impede coral resilience.